Methods, wireless device, network node and core node for managing reachability of the wireless device

ABSTRACT

A wireless device, a network node, a core node and methods therein, for managing reachability of the wireless device. The wireless device starts an AS (Access Stratum) reachable timer when entering an inactive state. If the AS reachable timer expires while still in the inactive state, the wireless device sends to the network node a reachable notification indicating that the wireless device is reachable. If entering a connected state before the AS reachable timer expires, the wireless device stops the AS reachable timer when changing from the inactive state to a connected state. If the core node receives from the network node a not reachable notification indicating that the wireless device is not reachable, the wireless device can be marked as not reachable via paging.

TECHNICAL FIELD

The present disclosure relates generally to a wireless device, a networknode, a core node, and methods therein, for managing reachability of thewireless device.

BACKGROUND

In this disclosure, the term “wireless device” is sometimes used torepresent any communication entity capable of radio communication with aradio network by sending and receiving radio signals, such as e.g.mobile telephones, tablets, laptop computers and Machine-to-Machine,M2M, devices, also known as Machine Type Communication, MTC, devices.Another common generic term in this field is “User Equipment, UE” whichis frequently used herein as a synonym for wireless device. The termswireless device and UE are thus used interchangeably herein.

Further, the term “network node”, is used herein to represent any nodeof a radio access network, RAN, that is operative to communicate radiosignals with wireless devices. The network node in this disclosure mayrefer to a base station, radio node, evolved Node B, base transceiverstation, access point, etc., which communicates radio signals with thewireless device. The term “eNB” is frequently used herein to representthe network node described herein. The terms network node and eNB arethus used interchangeably herein.

Further, the term “core node”, is used herein to represent any node of acore network, CN, that is operative to provide communication withwireless devices. The core node in this disclosure is associated withthe RAN. The term Mobility Management Entity, “MME” is frequently usedherein to represent the core node. The terms core node and MME are thusused interchangeably herein.

FIG. 1 illustrates a communication scenario where a wireless device 100can communicate with a network node 102 of a RAN over a wireless RRCinterface.

The network node 102 can further communicate with a core node 104 of acore network over an S1 interface. This communication scenario may beapplicable to the examples, situations and embodiments described herein.

However, it is a problem that the network, e.g. the core node 104 andnetwork node 102, may not be aware of whether the wireless device 100currently can be reached or not, referred to as reachability, such aswhether the wireless device 100 is able to receive paging messages orthe like. Solutions of today for reaching a wireless device requiresubstantial signaling which consumes resources in the network and causesunwanted delays, particularly in paging procedures.

SUMMARY

It is an object of embodiments described herein to address at least someof the problems and issues outlined above. It is possible to achievethis object and others by using a wireless device, a network node, acore node, and methods therein, as defined in the attached independentclaims.

According to one aspect, a method is performed by a wireless device formanaging reachability of the wireless device, wherein the wirelessdevice is in ECM_CONNECTED state and has an ECM connection between anetwork node of a RAN (Radio Access Network) and a core node associatedwith the RAN. In this method the wireless device starts an AS (AccessStratum) reachable timer when entering an inactive state. When detectingin the inactive state that the AS reachable timer expires, the wirelessdevice sends to the network node a reachable notification indicatingthat the wireless device is reachable. Alternatively, when changing fromthe inactive state to a connected state before the AS reachable timerexpires, the wireless device stops the AS reachable timer.

According to another aspect, a wireless device is arranged to managereachability of the wireless device, where the wireless device is inECM_CONNECTED state and has an ECM connection between a network node ofa RAN and a core node associated with the RAN. The wireless device isconfigured to start an AS reachable timer when entering an inactivestate, and to send to the network node a reachable notificationindicating that the wireless device is reachable when detecting in theinactive state that the AS reachable timer expires, or stop the ASreachable timer when changing from the inactive state to a connectedstate before the AS reachable timer expires.

According to another aspect, a method is performed by a network node ofa RAN, for managing reachability of a wireless device, wherein thewireless device is in ECM_CONNECTED state and has an ECM connectionbetween the network node and a core node associated with the RAN. Inthis method, the network node detects that the wireless device enters aninactive state and starts an AS reachable timer. When receiving from thewireless device a reachable notification indicating that the wirelessdevice is reachable, the network node restarts the AS reachable timer,or when detecting that the wireless device has changed from the inactivestate to a connected state, the network node stops the AS reachabletimer, or when detecting that the AS detach timer expires the networknode starts an AS detach timer and disconnecting the ECM connectionbetween the network node and the core node.

According to another aspect, a network node of a RAN is arranged tomanage reachability of a wireless device, where the wireless device isin ECM_CONNECTED state and has an ECM connection between the networknode and a core node associated with the RAN. The network node isconfigured to detect that the wireless device enters an inactive state,and to start an AS reachable timer. The network node is furtherconfigured to restart the AS reachable timer when receiving from thewireless device a reachable notification indicating that the wirelessdevice is reachable, or stop the AS reachable timer when detecting thatthe wireless device has changed from the inactive state to a connectedstate, or start an AS detach timer and disconnecting the ECM connectionbetween the network node and the core node when detecting that the ASdetach timer expires.

According to another aspect, a method is performed by a core nodeassociated with a RAN, for managing reachability of a wireless device,wherein the wireless device is in ECM_CONNECTED state and has an ECMconnection between a network node of the RAN and the core node. In thismethod, the core node receives from the network node a not reachablenotification indicating that the wireless device is not reachable,wherein the wireless device can be marked as not reachable via paging.

According to another aspect, a core node associated with a RAN isarranged to manage reachability of a wireless device, wherein thewireless device is in ECM_CONNECTED state and has an ECM connectionbetween a network node of the RAN and the core node. The core node isconfigured to receive from the network node a not reachable notificationindicating that the wireless device is not reachable, wherein thewireless device can be marked as not reachable via paging.

The above wireless device, network node, core node and methods may beconfigured and implemented according to different optional embodimentsto accomplish further features and benefits, to be described below.

BRIEF DESCRIPTION OF DRAWINGS

The solution will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a communication scenario illustrating a wireless devicecommunicating with a network node over a wireless RRC interface and thenetwork node communicating with a core node over an S1 interface, wherethe solution may be employed.

FIG. 2 is an example of a management system for node elements NEs, e.g.base stations, which are managed by domain managers DMs further managedby a network manager NM, where the solution may be employed.

FIG. 3 is a signaling diagram illustrating a current signaling procedurerequired to establish and tear down a connection between a UE and aneNB, according to the prior art.

FIG. 4 is another signaling diagram illustrating a signaling procedurefor a UE and an eNB with enhancements enabling the UE to resume an RRCconnection when returning from IDLE state, according to the prior art.

FIG. 5 is a flow chart illustrating a procedure in a wireless device,according to some example embodiments.

FIG. 6 is a flow chart illustrating a procedure in a network node,according to further example embodiments.

FIG. 7 is a block diagram illustrating how a wireless device, a networknode and a core node may be structured, according to further exampleembodiments.

FIG. 8 is a signaling diagram illustrating an example of a procedurewhen the solution is used, according to further example embodiments.

FIG. 9 is a signaling diagram illustrating another example of aprocedure when the solution is used, according to further exampleembodiments.

FIG. 10 is a signaling diagram illustrating another example of aprocedure when the solution is used, according to further exampleembodiments.

DETAILED DESCRIPTION

The third generation partnership project (3GPP) is currently working onstandardization of Release 13 of the Long Term Evolution (LTE) concept.The architecture of the LTE system includes radio access nodes (eNBs,Home eNBs—HeNBs, HeNB GW) and evolved packet core nodes (MME/S-GW). Inthe LTE architecture, an S1 interface connects HeNBs/eNBs to theMME/S-GW and HeNBs to the HeNB GW, while an X2 interface connects peereNBs/HeNBs, optionally via an X2 GW.

A management system that may be used when employing the proceduresdescribed herein is shown in FIG. 2. The node elements (NE), alsoreferred to as eNodeB, are managed by a domain manager (DM), alsoreferred to as the operation and support system (OSS). A DM may furtherbe managed by a network manager (NM). Two NEs are interfaced by X2,whereas the interface between two DMs is referred to as Itf-P2P. Themanagement system may configure the network elements, as well as receiveobservations associated to features in the network elements. Forexample, DM observes and configures NEs, while NM observes andconfigures DM, as well as NE via DM.

By means of configuration via the DM, NM and related interfaces,functions over the X2 and S1 interfaces can be carried out in acoordinated way throughout the RAN, eventually involving the CoreNetwork, i.e. MME and S-GWs.

Details on UE reachability management in ECM-IDLE can be found in 3GPPTS 23.401. A brief summary is described below.

As UE entered ECM-IDLE state, its location is known by the network on aTracking Area List granularity. All cells of the Tracking Areas in whicha UE in ECM-IDLE/EMM-REGISTERED is currently registered needs to betaken into account for paging. However, UE also needs to notify thenetwork its availability periodically. Therefore, a periodic TrackingArea Update, TAU, timer (T3412) is used by UE performing periodicTracking Area Updates with the network after the expiry of the timer.

The MME may allocate long periodic TAU timer value to the UE. Typically,this periodic TAU timer value is sent in ATTACH ACCEPT and/or TRACKINGAREA UPDATE ACCEPT messages.

If the UE is out of E-UTRAN coverage when its periodic TAU timerexpires, the UE shall:

-   -   if ISR (Idle Mode Signalling Reduction) is activated, start the        E-UTRAN Deactivate ISR timer. After the E-UTRAN Deactivate ISR        timer expires the UE shall deactivate ISR.    -   when EMM-REGISTERED, perform a Tracking Area Update when it next        returns to E UTRAN coverage.

The E-UTRAN Deactivate ISR timer is stopped when the UE performs asuccessful Tracking Area Update.

The UE's periodic TAU timer is restarted from its initial value wheneverthe UE enters ECM IDLE mode.

Typically, the MME runs a mobile reachable timer. Whenever the UE entersECM IDLE mode the timer is started with a value similar to the UE'speriodic TAU timer. If this timer expires in the MME, the MME can deducethat the UE is not reachable. However, the MME does not know for howlong the UE is not reachable, so, the MME shall not immediately deletethe UE's bearers. Instead the

MME should clear the PPF (Page Proceed Flag) in the MME and start anImplicit Detach timer, with a relatively large value and if ISR isactivated, at least slightly larger than the UE's E-UTRAN Deactivate ISRtimer.

If MME has allocated an Active Time to the UE, then the MME starts theActive timer with the value of Active Time whenever the UE enters ECMIDLE mode. If this timer expires in the MME, the MME can deduce that theUE is not reachable and should clear the PPF in the MME.

With the PPF cleared, the MME does not page the UE in E UTRAN coverageand shall send a Downlink Data Notification Reject message to theServing GW when receiving a Downlink Data Notification message from theServing GW. If the

Implicit Detach timer expires before the UE contacts the network, thenthe MME can deduce that the UE has been ‘out of coverage’ for a longperiod of time and implicitly detach the UE.

LTE Architecture Evolution

It is not yet specified by 3GPP if and how the LTE architecture shouldevolve to meet the challenges of the 5G time frame.

It may however be assumed that there will be evolved counterparts of theS1, X2 and Uu interfaces and that any new Radio Access Technology, RATwould be integrated with the LTE radio interface at RAN level in asimilar fashion as the way LTE Dual Connectivity is defined.

The embodiments and examples described herein may be useful for both anLTE-like architecture and a new architecture based on an evolution ofthe S1 interface, also referred to as an S1 connection.

RRC Suspension and Inactive State

In 3GPP document R3-160845, there is a description on RRC suspensionprinciple.

In current Evolved Packet System, EPS networks, the main contributors tothe signalling overhead and load are procedures used for UE statetransition, i.e. at transition between the Idle and the connectedstates.

FIG. 3 illustrates the current S1/EPS architecture based proceduresrequired to establish and tear down a connection in order for the UE tobe able to transfer/receive user plane data, i.e. procedures applicableat UE idle/connected state transition. As it can be seen in this figure,there is a significant amount of signalling overhead on the Uu (radio)and S1 interfaces required for small data transactions.

In order to reduce the signalling overhead and the associated processingload in the network, it has been proposed that a solution will beintroduced in Rel-13 that allows an RRC connection to be suspended andat a later time resumed; minimising the need to go through the fullsignalling procedure for setting up a new RRC connection upon idle toconnected state transition. The proposed solution is applicable both toLTE UEs and IoT (Internet of Things) UEs.

The proposed and adopted solution is based on enhancements to the IDLEstate to make it possible to resume the RRC connection avoiding the needto set it up again when the UE returns from IDLE, assuming that most ofthe times the UE returns in a node which has the stored RRC context. Theprocedure is illustrated in FIG. 4.

In the discussions on 5G system design, an evolution of thesuspend/resume technique has been proposed and is currently underevaluation. This proposal includes creating a new UE state, hereincalled Inactive State. This state is sometimes called dormant state ordormant mode or inactive mode. This state includes keeping the UE inRRC_IDLE, while a Control Plane (CP) and User Plane (UP) signalingconnection between RAN and CN is kept active for the UE. Therefore theUE appears as Connected/active from a CN point of view but it is Idlefrom an Access Stratum (AS) point of view. With this new state it hasnot been specified how reachability of the UE is achieved. As anexample, it may therefore not be possible for the core node to knowwhether the UE is reachable for paging.

Some problems with existing solutions may be as follows.

As RRC Inactive State is introduced, there will be no guarantee that theUE is reachable by RAN (or by the Core Network) when there is nodedicated RRC connection in between, also when the RRC connection issuspended, and the ECM is still in ECM_CONNECTED state. Therefore thereis a problem of activation of UE reachability management mechanismsbecause in legacy systems a UE that is in ECM_CONNECTED at the CN is notsupposed to perform any reachability updates. Therefore, additionalmechanisms for UE reachability management are needed.

In UTRAN, one solution to solve this problem is introducing a timer ontransition from URA_PCH state (similar to RRC suspended) to IDLE state.However, by introducing a similar solution the signaling overhead willincrease on the Uu (radio) and S1 interfaces, which is contrary to theobjection of reducing the signaling by RRC suspension and InactiveState.

The above problems may be addressed by employing at least some of theembodiments herein, as follows.

An example of how the solution may be employed in terms of actionsperformed by a wireless device such as the wireless device 100, will nowbe described with reference to the flow chart in FIG. 5, and withfurther reference to FIG. 1 as a non-limiting example. FIG. 5 thusillustrates a procedure in the wireless device 100 for managingreachability of the wireless device 100, wherein the wireless device 100is in ECM_CONNECTED state and has an ECM connection between a networknode 102 of a RAN (Radio Access Network) and a core node 104 associatedwith the RAN.

In a first action 500, the wireless device 100 starts an AS (AccessStratum) reachable timer when entering an inactive state. Depending onthe AS reachable timer and in which state the device is, either of thefollowing is performed. If the wireless device 100 detects in an action502 that the AS reachable timer expires while still in the inactivestate, another action 504 illustrates that the wireless device 100 sendsto the network node 102 a reachable notification indicating that thewireless device 100 is reachable.

As an alternative to actions 502 and 504, the wireless device 100 entersa connected state before the AS reachable timer expires, and anotheraction 506 illustrates that the wireless device 100 in this case stopsthe AS reachable timer when changing from the inactive state to aconnected state before the AS reachable timer expires.

Some example embodiments that could be used in this procedure will nowbe described. In one example embodiment, the wireless device 100 mayreceive a value of the AS reachable timer from the network node 102.Alternatively, this value may have been preconfigured in the wirelessdevice 100.

In some example embodiments, the wireless device 100 may restart the ASreachable timer after sending said reachable notification to the networknode 102 as of action 504, and also after receiving a reachablenotification acknowledgement from the network node 102, or when changingfrom the connected state to the inactive state.

In another example embodiment, the wireless device 100 may, after eitherof actions 504 and 506, start an AS (Access Stratum) detach timer whendetecting that the RAN is not reachable when the AS reachable timerexpires, as illustrated by an optional action 508. the wireless device100 may further change from the inactive state to ECM_IDLE state whendetecting that the AS detach timer expires, as illustrated by anotheroptional action 510. In another example embodiment, the wireless device100 may receive a value of the AS detach timer from the network node102. Alternatively, this value may have been preconfigured in thewireless device 100.

An example of how the solution may be employed in terms of actionsperformed by a network node such as the network node 102, will now bedescribed with reference to the flow chart in FIG. 6, and with furtherreference to FIG. 1. FIG. 6 thus illustrates a procedure in a networknode 102 of a RAN (Radio Access Network), for managing reachability of awireless device 100, wherein the wireless device 100 is in ECM_CONNECTEDstate and has an ECM connection between the network node 102 and a corenode 104 associated with the RAN.

In a first action 600, the network node 102 detects that the wirelessdevice 100 enters an inactive state. This triggers the network node 102to start an AS (Access Stratum) reachable timer in another action 602which corresponds to action 500 above. It should be noted that the ECMconnection between the network node 102 and the core node 104 can bemaintained and handled for the wireless device 100 as follows. Dependingon what happens next, the network node 102 will perform either of thefollowing alternative actions.

In one alternative action 604A, the network node 102 restarts the ASreachable timer when receiving from the wireless device 100 a reachablenotification indicating that the wireless device 100 is reachable.Thereby, the still existing

ECM connection is maintained and can be used for the wireless device 100in case it enters the connected state.

In another alternative action 604B, the network node 102 stops the ASreachable timer when detecting that the wireless device 100 has changedfrom the inactive state to a connected state. Thereby, the existing ECMconnection can be used for the wireless device 100 and it is notnecessary to set up a new ECM connection.

In another alternative action 604C, the network node 102 starts an AS(Access Stratum) detach timer and disconnects the ECM connection betweenthe network node 102 and the core node 104 when detecting that the ASdetach timer expires. The AS detach timer in this case thus controls howlong time the ECM connection between the network node 102 and a corenode 104 is maintained for the wireless device 100.

An example of how the solution may be employed in a procedure performedby a core node associated with a RAN, such as the core node 104, willnow also be described. This procedure is thus performed by the core node104 for managing reachability of a wireless device 100, wherein thewireless device 100 is in ECM_CONNECTED state and has an ECM connectionbetween a network node 102 of the RAN and the core node 104.

In this procedure, the core node 104 receives from the network node 102a not reachable notification indicating that the wireless device 100 isnot reachable, wherein the wireless device 100 can be marked as notreachable via paging. Marking, or noting, the wireless device 100 as notreachable may be done in different ways.

In one example embodiment, the core node 104 may mark the wirelessdevice 100 as not reachable via paging, by clearing a PPF (Page ProceedFlag) of the wireless device 100.

The block diagram in FIG. 7 illustrates a detailed but non-limitingexample of how a wireless device 700, a network node 702 and a core node704, respectively, may be structured to bring about the above-describedalternatives and embodiments thereof. In this figure, the wirelessdevice 700, the network node 702 and the core node 704 may be configuredto operate according to any of the alternatives and examples ofemploying the solution as described herein, where appropriate. Each ofthe wireless device 700, the network node 702 and the core node 704 isshown to comprise a processor “P”, a memory “M” and a communicationcircuit “C” with suitable equipment for transmitting and receivingmessages and signals in the manner described herein.

The communication circuit C in each of the wireless device 700, thenetwork node 702 and the core node 704 thus comprises equipmentconfigured for communication with each other using a suitable protocolfor the communication depending on the implementation. The solution ishowever not limited to any specific types of messages, signals orprotocols.

The wireless device 700 is arranged to manage reachability of thewireless device 700, when the wireless device 700 is in ECM_CONNECTEDstate and has an ECM connection between a network node 702 of a RAN(Radio Access Network) and a core node 704 associated with the RAN. Thewireless device 700 comprises a state module 700A configured to handlestates in the wireless device 700 as described herein. The wirelessdevice 700 also comprises a timer module 700B configured to handletimers as described herein. The wireless device 700 further comprises asending module 700C configured to send messages as described herein.

In more detail, the wireless device 700 is configured to start an AS(Access

Stratum) reachable timer when entering an inactive state, which timerstarting operation may be performed by the timer module 700B. Thewireless device 700 is further configured to send to the network node702 a reachable notification indicating that the wireless device 700 isreachable when detecting in the inactive state that the AS reachabletimer expires. This sending operation may be performed by the sendingmodule 700C. The wireless device 700 is further configured toalternatively stop the AS reachable timer when changing from theinactive state to a connected state before the AS reachable timerexpires. This timer stopping operation may be performed by the timermodule 700B.

The network node 702 belongs to a RAN and is arranged to managereachability of a wireless device 700, when the wireless device 700 isin ECM_CONNECTED state and has an ECM connection between the networknode 702 and a core node 704 associated with the RAN. The network node702 comprises a detecting module 702A configured to detect states in thewireless device 700 as described herein. The network node 702 alsocomprises a timer module 702B configured to handle timers as describedherein. The network node 702 further comprises a receiving/sendingmodule 702C configured to receive and send messages as described herein.The network node 702 also comprises a connection module 702D configuredto handle the ECM connection as described herein.

In more detail, the network node 702 is configured to detect that thewireless device 700 enters an inactive state, which detecting operationmay be performed by the detecting module 702A. The network node 702 isalso configured to start an AS reachable timer, which timer startingoperation may be performed by the timer module 702B.

Depending on the situation, the network node 702 is configured toperform either of the following operations. Firstly, the network node702 is configured to restart the AS reachable timer when receiving fromthe wireless device 700 a reachable notification indicating that thewireless device 700 is reachable. This timer restarting operation may beperformed by the timer module 702B.

Secondly, the network node 702 is configured to stop the AS reachabletimer when detecting that the wireless device 700 has changed from theinactive state to a connected state. This timer stopping operation maybe performed by the timer module 7026. Thirdly, the network node 702 isconfigured to start an AS (Access Stratum) detach timer and disconnectthe ECM connection between the network node 702 and the core node 704when detecting that the AS detach timer expires. This timer startingoperation and disconnecting operation may be performed by the timermodule 702B and by the connection module 702D, respectively.

The core node 704 is associated with a RAN and arranged to managereachability of a wireless device 700, when the wireless device 700 isin ECM_CONNECTED state and has an ECM connection between a network node702 of the RAN and the core node 704. The core node 704 comprises aconnection module 704A configured to handle the ECM connection asdescribed herein. The core node 704 also comprises a timer module 704Bconfigured to handle timers as described herein. The core node 704further comprises a receiving module 704C configured to receive messagesas described herein.

In more detail, the core node 704 is configured to receive from thenetwork node 702 a not reachable notification indicating that thewireless device 700 is not reachable. This receiving operation may beperformed by the receiving module 704C. Thereby, the wireless device 700can be marked as not reachable via paging.

The wireless device 700, the network node 702 and the core node 704 are,e.g. by means of units, modules or the like, configured or arranged toperform at least some of the actions and steps of the above-describedsignaling diagrams, where appropriate.

It should be noted that FIG. 7 illustrates various functional modules inthe wireless device 700, the network node 702 and the core node 704,respectively, and the skilled person is able to implement thesefunctional modules in practice using suitable software and hardwareequipment. Thus, the solution is generally not limited to the shownstructures of the wireless device 700, the network node 702 and the corenode 704, and the functional modules therein may be configured tooperate according to any of the features, examples and embodimentsdescribed in this disclosure, where appropriate.

The functional modules 700A-C, 702A-C and 704A-C may be implemented inthe wireless device 700, the network node 702 and the core node 704,respectively, by means of program modules of a respective computerprogram comprising code means which, when run by the processor P causesthe wireless device 700, the network node 702 and the core node 704 toperform the above-described actions and procedures. Each processor P maycomprise a single Central Processing Unit (CPU), or could comprise twoor more processing units. For example, each processor P may include ageneral purpose microprocessor, an instruction set processor and/orrelated chips sets and/or a special purpose microprocessor such as anApplication Specific Integrated Circuit (ASIC). Each processor P mayalso comprise a storage for caching purposes.

Each computer program may be carried by a computer program product ineach of the wireless device 700, the network node 702 and the core node704 in the form of a memory having a computer readable medium and beingconnected to the processor P. The computer program product or memory Min each of the wireless device 700, the network node 702 and the corenode 704 thus comprises a computer readable medium on which the computerprogram is stored e.g. in the form of computer program modules or thelike. For example, the memory M in each node may be a flash memory, aRandom-Access Memory (RAM), a Read-Only Memory (ROM) or an ElectricallyErasable Programmable ROM (EEPROM), and the program modules could inalternative embodiments be distributed on different computer programproducts in the form of memories within the respective wireless device700, network node 702 and core node 704.

The solution described herein may be implemented in each of the wirelessdevice 700, the network node 702 and the core node 704 by a computerprogram comprising instructions which, when executed on at least oneprocessor, cause the at least one processor to carry out the actionsaccording to any of the above embodiments and examples, whereappropriate. The solution may also be implemented at each of thewireless device 700, the network node 702 and the core node 704 in acarrier containing the above computer program, wherein the carrier isone of an electronic signal, optical signal, radio signal, or computerreadable storage medium.

Some further features and examples of how the above embodiments can beemployed in practice will now be described with reference to threedifferent communication cases illustrated by the signaling diagrams inFIGS. 8-10.

In the embodiments herein, a new dedicated AS timer for UE reachabilitymanagement can be employed in the RAN and in the UE when RRC isInactive. More specifically, the above-described two timers, referred toas “AS reachable timer” and “AS detach timer”, may be employed. Thisway, an RRC notification procedure is basically introduced between UEand eNB so that the UE is able to update the RAN about its reachability.

-   -   If RAN receives an RRC reachable signal from UE and if the        signaling exchange between RAN and UE is successful (it is        assumed that the UE receives confirmation of successful update        from the RAN), the AS reachable timer will be reset both at RAN        and UE. Eventually AS detach timer will be stopped.    -   When AS reachable timer expires on RAN and the RAN did not        receive any update signaling from the UE, RAN will notify CN to        clear the PPF, i.e. notify the UE is currently not reachable via        paging, and a AS detach timer will be started    -   When AS detach timer expires on RAN. RAN will terminate the ECM        connection and UP connection and notify CN for further actions.    -   When AS reachable timer expires on UE and is within RAN        coverage, it will initiate RRC reachable notification procedure.    -   When AS reachable timer expires on UE and is out of RAN coverage        or if a RRC reachable notification procedure is initiated and it        is not successful, the UE will initiate RRC reachable        notification procedure as soon as it is within RAN coverage,

By employing at least some of the above embodiments, the network is ableto determine the UE availability when the UE is in inactive state.

The three signalling diagrams in FIGS. 8-10 will now be described toillustrate the handling of three different situations A-C. Thesesituations represent the following:

A: Normal case, where the UE enters inactive state and starts itsperiodic timer, and the UE can successfully transmit a reachabilityresponse to the network after the periodic timer timeout occurs.

B: RRC in connected state before timeout, where the UE enters inactivestate and starts its periodic timer, but re-enters active state beforeperiodic timer timeout occurs.

C: UE not reachable and periodic timeout occurs, where the UE entersinactive state and starts its periodic timer, and the UE cannot transmita reachability response to the network after the periodic timeoutoccurs.

Throughout the following examples, the above-described ECM connectionbetween the network node and the core node is referred to as “the S1connection” for short.

FIG. 8 is a signalling diagram for situation A, “normal case”. In thisexample, the following actions are performed:

Action 8:1. A new AS reachable timer value is transferred from e(g)NB toUE prior UE enters RRC inactive state. This value can either betransferred by a new dedicated message or as a new IE on existingmessages through RRC.

Action 8:2. A new AS detach timer value is transferred from e(g)NB to UEprior UE enters RRC inactive state. This value can either be transferredby a new dedicated message or as a new IE on existing messages throughRRC.

Action 8:3. UE enters RRC inactive state due to inactivity on userplane. The RRC connection between eNB and UE will be released, but theS1 connection between eNB and MME will still be kept.

Action 8:4. e(g)NB starts a new AS reachable timer for the UE after theUE enters RRC inactive state.

Action 8:5. UE starts a new AS reachable timer after its RRC statechanges to inactive.

Action 8:6. The AS reachable timer timeout occurs on UE.

Action 8:7. UE transmits a new RRC signal, reachable notification,notifying e(g)NB its reachability.

Action 8:8. e(g)NB responses UE's reachable notification with a newacknowledgement signal through RRC.

Action 8:9. e(g)NB restarts the AS reachable timer for the UE afterreception of RRC signal “reachable notification” from UE.

Action 8:10. UE restarts the AS reachable timer for the UE afterreception of RRC signal “reachable notification acknowledgement” frome(g)NB.

FIG. 9 is a Sequence diagram for situation B, “RRC in connected statebefore timeout”, where the UE thus enters RRC connected state beforetimeout of the AS reachable timer. In this example, the followingactions are performed:

Action 9:1. A new AS reachable timer value is transferred from e(g)NB toUE prior UE enters RRC inactive state. This value can either betransferred by a new dedicated message or as a new IE on existingmessages through RRC.

Action 9:2. A new AS detach timer value is transferred from e(g)NB to UEprior UE enters RRC inactive state. This value can either be transferredby a new dedicated message or as a new IE on existing messages throughRRC.

Action 9:3. UE enters RRC inactive state due to inactivity on userplane. The RRC connection between eNB and UE will be released, but theS1 connection between eNB and MME will still be kept.

Action 9:4. e(g)NB starts a new AS reachable timer for the UE after theUE enters RRC inactive state.

Action 9:5. UE starts a new AS reachable timer after its RRC statechanges to inactive.

Action 9:6. UE changes its RRC state from inactive to connected, due toe.g. data activity on the user plane.

Action 9:7. e(g)NB stops the AS reachable timer for the UE after theUE's RRC state changes to connected.

Action 9:8. UE stops the AS reachable timer after its RRC state has beenchanged to connected.

FIG. 10 is a Sequence diagram for situation C, “UE not reachable andperiodic timeout occurs”, where the UE is thus not reachable when thetimeout of the AS reachable timer occurs. In this example, the followingactions are performed:

Action 10:1. A new AS reachable timer value is transferred from e(g)NBto UE prior UE enters RRC inactive state. This value can either betransferred by a new dedicated message or as a new IE on existingmessages through RRC.

Action 10:2. A new AS detach timer value is transferred from e(g)NB toUE prior UE enters RRC inactive state. This value can either betransferred by a new dedicated message or as a new IE on existingmessages through RRC.

Action 10:3. UE enters RRC inactive state due to inactivity on userplane. The RRC connection between eNB and UE will be released, but theS1 connection between eNB and MME will still be kept.

Action 10:4. e(g)NB starts a new AS reachable timer for the UE after theUE enters RRC inactive state.

Action 10:5. UE starts a new AS reachable timer after its RRC statechanges to inactive.

Action 10:6. Network is not reachable from UE and it cannot notifye(g)NB its reachability.

Action 10:7. The AS reachable timer for the UE gets timeout on e(g)NB.

Action 10:8. e(g)NB notifies MME that the UE is unreachable through anew S1AP procedure. The S1 connection for the UE is kept.

Action 10:9. MME marks the UE as unreachable, i.e. no paging will beperformed on the UE if DL data for the UE arrives to the core network.

Action 10:10. e(g)NB starts a new AS detach timer for the UE after ASreachable timer timeout for the UE occurs.

Action 10:11. The AS reachable timer timeout occurs on UE.

Action 10:12. As UE cannot reach the network and AS reachable timertimeout occurs, UE starts a new AS detach timer.

Action 10:13. The AS detach timer for the UE gets timeout on e(g)NB.

Action 10:14. e(g)NB initiates S1 disconnection between core network ande(g)NB for the UE, and set the connection between UE and network toECM_IDLE. After this point the UE reachability procedure is taken overby the MME/Core network.

Action 10:15. The AS detach timer timeout occurs on UE

Action 10:16. UE will change its ECM state to ECM_IDLE.

While the solution has been described with reference to specificexemplifying embodiments, the description is generally only intended toillustrate the inventive concept and should not be taken as limiting thescope of the solution. For example, the terms “network node”, “wirelessdevice”, “core node”, “ECM connection”, “NAS periodic timer”, “ASreachable timer”, and “AS detach timer” have been used throughout thisdisclosure, although any other corresponding entities, functions, and/orparameters could also be used having the features and characteristicsdescribed here. The solution may be implemented according to theappended claims.

1. A method performed by a wireless device for managing reachability ofthe wireless device, wherein the wireless device is in ECM_CONNECTEDstate and has an ECM connection between a network node of a RAN (RadioAccess Network) and a core node associated with the RAN, the methodcomprising: starting an AS (Access Stratum) reachable timer whenentering an inactive state, and sending to the network node a reachablenotification indicating that the wireless device is reachable whendetecting in the inactive state that the AS reachable timer expires, orstopping the AS reachable timer when changing from the inactive state toa connected state before the AS reachable timer expires.
 2. A methodaccording to claim 1, wherein a value of the AS reachable timer isreceived from the network node.
 3. A method according to claim 1,wherein the AS reachable timer is restarted in the wireless device aftersending said reachable notification to the network node and receiving areachable notification acknowledgement from the network node, or whenchanging from the connected state to the inactive state.
 4. A methodaccording to claim 1, the method further comprising: starting an AS(Access Stratum) detach timer when detecting that the RAN is notreachable and the AS reachable timer expires, and changing from theinactive state to ECM_IDLE state when detecting that the AS detach timerexpires.
 5. A method according to claim 4, wherein a value of the ASdetach timer is received from the network node.
 6. A method performed bya network node of a RAN (Radio Access Network), for managingreachability of a wireless device, wherein the wireless device is inECM_CONNECTED state and has an ECM connection between the network nodeand a core node associated with the RAN, the method comprising:detecting that the wireless device enters an inactive state, starting anAS (Access Stratum) reachable timer, and restarting the AS reachabletimer when receiving from the wireless device a reachable notificationindicating that the wireless device is reachable, or stopping the ASreachable timer when detecting that the wireless device has changed fromthe inactive state to a connected state, or starting an AS (AccessStratum) detach timer and disconnecting the ECM connection between thenetwork node and the core node when detecting that the AS detach timerexpires.
 7. A method performed by a core node associated with a RAN(Radio Access Network), for managing reachability of a wireless device,wherein the wireless device is in ECM_CONNECTED state and has an ECMconnection between a network node of the RAN and the core node, themethod comprising: receiving from the network node a not reachablenotification indicating that the wireless device is not reachable,wherein the wireless device can be marked as not reachable via paging.8. A method according to claim 7, wherein the wireless device is markedas not reachable via paging, by clearing a PPF (Page Proceed Flag) ofthe wireless device.
 9. A wireless device for managing reachability ofthe wireless device, when the wireless device is in ECM_CONNECTED stateand has an ECM connection between a network node of a RAN (Radio AccessNetwork) and a core node associated with the RAN, wherein the wirelessdevice is configured to: start an AS (Access Stratum) reachable timerwhen entering an inactive state, and send to the network node areachable notification indicating that the wireless device is reachablewhen detecting in the inactive state that the AS reachable timerexpires, or stop the AS reachable timer when changing from the inactivestate to a connected state before the AS reachable timer expires.
 10. Awireless device according to claim 9, wherein the wireless device isconfigured to receive a value of the AS reachable timer from the networknode.
 11. A wireless device according to claim 9, wherein the wirelessdevice is configured to restart the AS reachable timer in the wirelessdevice after sending said reachable notification to the network node andreceiving a reachable notification acknowledgement from the network nodeor when changing from the connected state to the inactive state.
 12. Awireless device according to claim 9, wherein the wireless device isfurther configured to: start an AS (Access Stratum) detach timer whendetecting that the RAN is not reachable and the AS reachable timerexpires, and change from the inactive state to ECM_IDLE state whendetecting that the AS detach timer expires.
 13. A wireless deviceaccording to claim 12, wherein a value of the AS detach timer isreceived from the network node.
 14. A network node of a RAN (RadioAccess Network), for managing reachability of a wireless device, whenthe wireless device is in ECM_CONNECTED state and has an ECM connectionbetween the network node and a core node associated with the RAN,wherein the network node is configured to: detect that the wirelessdevice enters an inactive state, start an AS (Access Stratum) reachabletimer, and restart the AS reachable timer when receiving from thewireless device a reachable notification indicating that the wirelessdevice is reachable, or stop the AS reachable timer when detecting thatthe wireless device has changed from the inactive state to a connectedstate, or start an AS (Access Stratum) detach timer and disconnectingthe ECM connection between the network node and the core node whendetecting that the AS detach timer expires.
 15. A core node associatedwith a RAN (Radio Access Network), for managing reachability of awireless device, wherein the wireless device is in ECM_CONNECTED stateand has an ECM connection between a network node of the RAN and the corenode, wherein the core node is configured to: receive from the networknode a not reachable notification indicating that the wireless device isnot reachable, wherein the wireless device can be marked as notreachable via paging.
 16. A core node according to claim 15, wherein thecore node is configured to mark the wireless device as not reachable viapaging, by clearing a PPF (Page Proceed Flag) of the wireless device.17. A computer program comprising instructions which, when executed onat least one processor, cause the at least one processor to carry outthe method according to claim
 1. 18. A carrier containing the computerprogram of claim 17, wherein the carrier is one of an electronic signal,optical signal, radio signal, or computer readable storage medium.